Transcript Review Organic Chemistry Chemistry 203

Chemistry 203
Review
Organic Chemistry
Bonding
Goal of atoms
Filled valence level
1. Ionic bonds
2. Covalent bonds
Noble gases
(Stable)
Bonding
Ionic bonds
result from the transfer of electrons from one element to another.
Cation (Y+)
Metals: lose 1, 2 or 3 e-
Ions
Nonmetals: gain 1, 2 or 3 e-
Anion (X-)
Cation (Y+):
Na+
Li+
Ca2+
Anion (X-):
Cl-
F-
O2-
Al3+
Bonding
Ionic bonds
Metal-Nonmetal
Cl: 1s2 2s2 2p6 3s2 3p5
Na: 1s2 2s2 2p6 3s1
Na+:
-
Cl : 1s2 2s2 2p6 3s2 3p6
1s2 2s2 2p6
Ne
Cation
Ar
Anion
Bonding
Covalent bonds
result from the sharing of electrons between two atoms.
Nonmetal-Nonmetal
Metalloid-Nonmetal
Sharing of
valence electrons
Lewis Dot Structure
H
Li
He
Al
C
N
Cl
Lewis Structure
H H
Or
H
H
Cl
Or
Cl
H
H
Cl: 1s2 2s2 2p6 3s2 3p5
H: 1s1
Ar: 1s2 2s2 2p6 3s2 3p6
He: 1s2
Intermolecular Forces
London dispersion forces
Intermolecular
Forces
Dipole-dipole interaction
<
Ionic bonds
Covalent bonds
Intramolecular
(Bonding) Forces
Hydrogen bonding
London dispersion forces
Attractive forces between all molecules
Only forces between nonpolar covalent molecules
_
He
He
2+ _
2+ _
_
He
δ-
_
_
δ+
2+
Original Temporary
Dipole
No Polarity
He
δ-
_
_
δ+
2+
Original Temporary
Dipole
He
δ-
_
_
δ+
2+
Induced Temporary
Dipole
He
+
_
2+
_
London dispersion forces
He:
T↓
Kinetic energy ↓
Move slower
T = -240°C (1 atm) → liquid
Attractive forces
become more important
liquid
Dipole-Dipole Interactions
Attractive forces between two polar molecules
stronger than London dispersion forces
boiling point ↑
Hydrogen bonding
Between H bonded to O, N, or F (high electronegativity) → δ+
and a nearby O, N, or F → δhydrogen
bond
H
-
O

+
H
H
O
H
H 2O
(a)
Stronger than dipole-dipole interactions & London dispersion forces
Hydrogen bonding
δ+
CH3COOH
Acetic acid
δ-
H-bonding in our body
H-bond
H-bond
Protein (α-helix)
DNA
Intermolecular Forces
Solubility
polar dissolves polar
like dissolves like
Nonpolar dissolves nonpolar
octane
CCl4
octane + CCl4
Organic Compounds
Hydrocarbons
Large family of organic compounds
Composed of only carbon and hydrogen
Saturated hydrocarbons
Unsaturated hydrocarbons
Alkanes
H
Alkenes, Alkynes
& Aromatics
H
C-C
C=C
H
C
C
C
C
C
H
CC C
H
Alkanes
Chemical reactions of Alkanes
Low reactivity
1- Combustion:
• Alkanes react with oxygen.
• CO2, H2O, and energy are produced.
• Alkane + O2
CH4 + 2O2
CO2 + H2O + heat
CO2 + 2H2O + energy
Chemical reactions of Alkanes
Low reactivity
2- Halogenation:
Alkanes react with Halogens.
CH4 + Cl2
CH3Cl + HCl
Chloromethane
CH2Cl2 + HCl
Dichloromethane
CHCl3 + HCl
Trichloromethane
CCl4 + HCl
Tetrachloromethane
Heat or light
CH3Cl+ Cl2
Heat or light
CH2Cl2+ Cl2
Heat or light
CHCl3+ Cl2
Heat or light
Alkenes
&
Alkyens
Chemical properties of Alkenes & Alkynes
More reactive than Alkanes
Addition of Hydrogen (Hydrogenation-Reduction)
Addition of Hydrogen Halides (Hydrohalogenation)
Addition of water (Hydration)
Addition of Bromine & Chlorine (Halogenation)
Chemical properties of Alkenes & Alkynes
Addition reactions
–C = C –
– C – C–
Exothermic reactions
Products are more stable (have the lower energy).
Chemical properties of Alkenes & Alkynes
More reactive than Alkanes
1. Hydrogenation (Reduction):
• A hydrogen atom adds to each carbon atom of a double
bond.
• A catalyst such as platinum or palladium is used (Transition metals).
H H
│ │
H–C=C–H + H2
Ethene
Pt
Pt
H
H
│
│
H– C – C– H
│
│
H
H
Ethane
Chemical properties of Alkenes & Alkynes
More reactive than Alkanes
2. Hydrohalogenation:
• A hydrogen halide (HCl, HBr, or HI) adds to alkene to
give haloalkane.
H H
H
H
│ │
│
│
H–C=C–H + HCl
Ethene
H– C – C– H
│
│
H
Cl
Chloroethane
Chemical properties of Alkenes & Alkynes
2. Hydrohalogenation:
- reaction is regioselective.
- Markovnikov’s rule: H adds to double bonded carbon that
has the greater number of H and halogen adds to the other carbon.
CH3 CH=CH2 + HCl
Prop ene
Cl H
CH 3 CH-CH2
H Cl
CH3 CH-CH2
2-Ch loroprop ane
1-Chlorop ropan e
(not formed)
The rich get richer!
Chemical properties of Alkenes & Alkynes
3. Hydration (addition of water):
• Water adds to C=C to give an alcohol.
• Acid catalyst (concentrated sulfuric acid).
• A regioselective reaction (Markovnikov’s rule).
CH3 CH=CH2
Propene
CH3
CH3 C=CH2
+
+
2-Methylp ropen e
H2 O
H2 O
H2 SO4
OH H
CH3 CH-CH2
2-Propan ol
CH3
H2 SO4
CH3 C-CH2
HO H
2-Methyl-2-prop anol
Chemical properties of Alkenes & Alkynes
More reactives than Alkanes
4. Halogenation:
• A halogen atom adds to each carbon atom of a double
bond.
• Usually by using an inert solvent like CH2Cl2.
H H
│ │
CH3–C=C–CH3 + Cl2
2-Butene
CH2Cl2
H
H
│
│
CH3– C – C– CH3
│
│
Cl
Cl
2,3-dichlorobutane
Aromatic Hydrocarbons
Chemical properties of aromatics
No addition reactions (almost unreactive)
Aromatic substitution: One of the H atoms is repalecd by some groups.
Halogenation
Nitration
Sulfonation
Chemical properties of benzene
1. Halogenation:
Cl and Br react rapidly with benzene in the presence of an iron catalyst.
H + Cl2
Benzen e
FeCl3
Cl + HCl
Chlorobenzene
Chemical properties of benzene
2. Nitration:
In presence of concentrated nitric acid and sulfuric acid,
one of the H atoms is replaced by a nitro (-NO2) group.
H + HNO3
H2 SO4
NO2 + H2 O
N itrob enzene
Chemical properties of benzene
3. Sulfonation:
In presence of concentrated sulfuric acid and heat,
one of the H atoms is replaced by sufonic acid (-SO3H)
group.
H + H2 SO4
Heat
SO3 H + H2 O
Benzenes ulfon ic acid
Alcohols
OH
OH + NaOH
Phenol
H2 O
O- Na+
+
S od ium phenoxide
(a w ater-soluble salt)
Chemical Properties of Alcohols
1. Acidity of Alcohols:
H2 O
OH + NaOH
Phenol
O- Na+ + H2 O
S od ium phenoxide
(a w ater-soluble salt)
2. Acid-Catalyzed Dehydration:
CH3CH2OH
-C–CH OH
H2SO4
180°C
CH2 = CH2 + H2O
Dehydration
Hydration
C = C + H20
3. Oxidation of Alcohols:
Acid-Catalyzed Dehydration
Alkene having the greater number of alkyl groups on the double bond
generally predominates.
OH
CH3 CH2 CHCH3
2-Butanol
H3 PO4
-H2 O
CH3 CH=CHCH3 + CH3 CH2 CH=CH2
2-Bu tene
(80%)
1-Butene
(20%)
CH3
CH3
CH3
H2 SO4
CH3 CHCHCH3
CH3 C=CHCH3 + CH3 CHCH=CH2
-H2 O
OH
3-Meth yl-2-b utanol
2-Methyl-2-b utene 3-Methyl-1-bu tene
(major prod uct)
Oxidation of 1° Alcohols
In the oxidation [O] of a primary alcohol 1, one H is
removed from the –OH group and another H from the C
bonded to the –OH.
primary alcohol
OH
│
CH3─C─H
│
H
ethanol
(ethyl alcohol)
[O]
K2Cr2O7
H2SO4
aldehyde
O
║
CH3─C─H + H2O
ethanal
(acetaldehyde)
Oxidation of 2° Alcohols
The oxidation of 2 alcohols is similar to 1°, except that a
ketone is formed.
[O]
secondary alcohol
OH
│
CH3─C─CH3
│
H
2-propanol
K2Cr2O7
H2SO4
ketone
O
║
CH3─C─CH3 + H2O
2-propanone
Oxidation of 3° Alcohols
Tertiary 3 alcohols cannot be oxidized.
Tertiary alcohol
OH
│
CH3─C─CH3
[O]
no reaction
K2Cr2O7
H2SO4
no product
│
CH3
no H on the C-OH to oxidize
2-methyl-2-propanol
Thiols
Chemical Properties of Thiols
1. Thiols are weak acids (react with strong bases).
CH3CH2SH + NaOH
H2O
CH3CH2S-Na+ + H2O
Sodium ethanethiolate
2. Oxidation to disulfides:
-S-S- disulfide
Oxidation
2HOCH3CH2SH + O2
Reduction
HOCH2CH2S-SCH2CH2OH
Amines
NH
CH22 CH3
CH3-NH2
C
CH3-NH-CH3
Eth ylb enzene
Tolu
Chemical properties of Amines
They are weak bases (like ammonia): react with acids.
(to form water-soluble salts)
H
CH3
N..
+
..
H – ..
O–H
H
CH3
H
N
+
-...
. ..O – H
H
H
(a) (CH3 CH2 ) 2 NH + HCl
+
-
(CH3 CH2 ) 2 NH2 Cl
D ieth ylammoniu m
chloride
CH3 COO-
+ CH3 COOH
(b)
N
N+
H
Pyridinium acetate
Aldehydes
&
Ketones
Chemical properties of Aldehydes and Ketones
1. Oxidation: only for aldehydes (not for ketones).
O
O
CH3─CH2─CH2─CH2─C─H
=
=
K2Cr2O7
CH3─CH2─CH2─CH2─C─OH
H2SO4
Pentanal
Pentanoic acid
K2Cr2O7: Oxidizing agent
Liquid aldehydes
are sensetive to oxidation.
O
C
2
H
O
C
+ O2
2
OH
No oxidizing agent
Benzaldehyde
Benzoic acid
Chemical properties of Aldehydes and Ketones
2. Reduction:
Like reducing the alkene (C = C) to alkane (C – C):
– Reduction of an aldehyde gives a primary alcohol (-CH2OH).
– Reduction of a ketone gives a secondary alcohol (-CHOH-).
=
O
+ H2
Pentanal
1-Pen tan ol
=
O
CH3─C─CH2─CH3
2-butanone
CH3─CH2─CH2─CH2─CH2─ OH
+ H
2
tran si ti o n
m etal catal y st
OH
-
CH3─CH2─CH2─CH2─C─ H
tran si ti on
metal cataly st
CH3─CH─CH2─CH3
2-butanol
Chemical properties of Aldehydes and Ketones
3. Addition of alcohols (hemiacetals):
H of the alcohol adds to the carbonyl oxygen and
OR adds to the carbonyl carbon.
O
H
C + O-CH2 CH3
H
Benzald ehyde Eth anol
O-H
C OCH2 CH3
H
A hemiacetal
unstable
Chemical properties of Aldehydes and Ketones
3. Addition of alcohols (Acetals):
O-H
Acid
C OCH2 CH3 + H O-CH 2 CH 3
H
A hemiacetal
Ethanol
O CH2CH3
C OCH2 CH3 + H2O
H
An Acetal
Chemical properties of Aldehydes and Ketones
3. Addition of alcohols (hemiacetals):
If –OH is part of the same molecule that contains C=O.
O
5
4
3
2
1
H
O-H
4-Hyd roxypentanal
redraw to
show the -OH
an d -CHO clos e
to each oth er
3
2
1
4
5
O
H
C
H
O
H
O-H
O
A cyclic hemiacetal
Carboxylic Acids
carbonyl group
O

CH3 — C—OH hydroxyl
Carboxyl group
Chemical properties of Carboxylic Acids
1- Reaction with bases:
COOH + NaOH
H2 O
Ben zoic acid
(slightly soluble in w ater)
COOH +
+
COO Na + H2 O
Sodiu m b enzoate
(60 g/100 mL w ater)
NH3
Benzoic acid
(s ligh tly solub le in w ater)
H2 O
-
COO NH4
+
Ammoniu m b enzoate
(20 g/100 mL water)
Chemical properties of Carboxylic Acids
2- Reduction:
Resistant to reduction
Using a powerful reducing agent: LiAlH4 (Lithium aluminum hydride).
1° alcohol
O
COH
3-cyclopentenecarboxylic acid
LiAlH4, ether
H2O
CH2OH
4-Hydroxymethylcyclopentene
Chemical properties of Carboxylic Acids
3- Fischer Esterification:
- A carboxylic acid reacts with an alcohols to form an ester.
- Using an acid catalyst such as concentrated sulfuric acid.
O
H2 SO4
CH3 C-OH + H-OCH2 CH3
Eth anoic acid
Ethanol
(Acetic acid) (Ethyl alcohol)
O
CH3 COCH2 CH3 + H2 O
Ethyl ethanoate
(Ethyl acetate)
The best way to prepare an ester.
Chemical properties of Carboxylic Acids
4- Decarboxylation:
Loss of CO2 from a carboxyl group.
O
RCOH
decarboxylation
Heat
RH +
CO 2
Esters
&
Amides
O
CH3 — C — NH2
Amide group
Formation of Esters
O
RCO H
A carboxylic acid
Fischer Esterification
O
RC- OH H-OR'
A carboxylic acid
An alcohol
H2SO4
O
RCOR' + H2O
An ester
Chemical Reactions of Esters
1. Hydrolysis: reaction with water.
(breaking a bond and adding the elements of water)
O
RCOR' + H2O
An ester
Heat
Acid
O
RC- OH
A carboxylic acid
+
H-OR'
An alcohol
Chemical Reactions of Esters
2. Saponification (Hydrolysis): an ester reacts with a hot aqueous base.
O
RCOR' + NaOH
Heat
H2O
An ester
O
CH3COCH2CH3 + NaOH
Ethyl Ethanoate
O
+
RCO-Na +
A sodium salt
H- OR'
An alcohol
O
- +
CH3CO-Na + CH3CH2OH
Sodium acetate
Ethanol
Chemical Reactions of Esters
3. Esters react with ammonia and with 1° and 2° amines to form
amides.
O
O
OCH2 CH3 + N H3
Ethyl 2-phenyl acetate
N H2 + CH3 CH2 OH
2-Phenylacetamide
Thus, an amide can be prepared from a carboxylic acid by first converting
the carboxylic acid to an ester by Fischer esterification and then reaction of
the ester with an amine.
Formation of Amides
O
RCO H
A carboxylic acid
O
RC- OH H-NHR'
A carboxylic acid
An Amine
O
CH3 C- OH + HHNCH2 CH3
Acetic acid
Ethanamine
Heat
O
RCNHR' + H2O
An amide
O
CH3 C- NHCH2 CH3 + H2 O
N-ethylethanamide
Chemical Reactions of Amides
Such as esters:
Hydrolysis in hot aqueous acid or base.
O
CH3 CH2 CH2 CNH2 + H2 O + HCl
H2 O
heat
Butanamide
O
CH3 CNH
A cetanilide
+ NaOH
H2 O
heat
O
+ CH3 CH2 CH2 COH + NH4 Cl
Butanoic acid
O
+
CH3 CO Na + H2 N
Sodiu m
acetate
Aniline
Chemical Reactions of Amides
Amides do not react with ammonia or with amines.